In colourimetry, the Munsell colour system is a colour system that specifies colours based on three colour dimensions, hue, lightness (called Value by Munsell), and Chroma (difference from gray at a given hue and lightness).

Professor Albert H. Munsell , an artist, wanted to create a "rational way to describe colour" that would use decimal notation instead of colour names (which he felt were "foolish" and "misleading"). He first started work on the system in 1898 and published it in full form in Colour Notation in 1905. The newer Munsell Book of Colour continues to be used today.

The system consists of an irregular cylinder with the value axis (light/dark) running up and down through it, as does the axis of the earth. Dark colours are at the bottom of the tree and light at the top, measured from 1 (dark) to 10 (light).

Each horizontal "slice" of the cylinder across the axis is a hue circle, which he divided into five principal hues: red, yellow, green, blue, and purple, five intermediates, yellow-red, green-yellow, blue-green, purple-blue, and red-purple. Munsell hue is specified by selecting one of these ten hues, and then referring to the angle inside them from 1 to 10.

"Chroma" was measured out from the center of the wheel, with lower chroma being less saturated (washed out, such as pastels). Note that there is no intrinsic upper limit to chroma. Different areas of the colour space have different maximal chroma coordinates. For instance light yellow colours have considerably more potential chroma than light purples, due to the nature of the eye and the physics of colour stimuli. This led to a wide range of possible chroma levels, and a chroma of 10 may or may not be maximal depending on the hue and value.

A colour is fully specified by listing the three numbers. For instance a fairly saturated blue of medium lightness would be 5B 5/10 with 5B meaning the colour in the middle of the blue hue band, 5/ meaning medium lightness, and a chroma of 10.

The original embodiment of the system (the 1905 Atlas) had some deficiencies as a physical representation of the theoretical system. These were improved significantly in the 1929 Munsell Book of Colour and through an extensive series of experiments carried out by the Optical Society of America in the 1940's resulting in the notations (sample definitions) for the modern Munsell Book of Colour. The system is still widely used in a variety of applications and represents one of the best available data sets on the perceptual scaling of lightness, chroma and hue. Several modern systems of colour measurement are built upon the foundation of the Munsell system.